1. Field of the Invention
The present invention relates to elastic wave devices in which a surface acoustic wave chip including a piezoelectric substrate is mounted on a package board.
2. Description of the Related Art
Hitherto, various kinds of elastic wave devices in which a surface acoustic wave chip is mounted on a package board have been proposed. For example, in Japanese Unexamined Patent Application Publication No. 2006-101550, two surface acoustic wave chips having different frequency characteristics are mounted on a package board by flip chip bonding. Each surface acoustic wave chip includes a piezoelectric substrate that is cut out of a single crystal having X, Y, and Z crystal axes. A long side of the surface acoustic wave chip extends along a direction where the coefficient of linear expansion of the surface acoustic wave chip has a value close to the coefficient of linear expansion of the package. The two surface acoustic wave chips are disposed so that the long sides thereof oppose each other.
In Japanese Unexamined Patent Application Publication No. 2012-205215, a transmission filter chip and a reception filter chip configured of respective surface acoustic wave filter chips are mounted on a package board. A propagation direction of the surface acoustic wave of the transmission filter chip is the same as a propagation direction of the surface acoustic wave of the reception filter chip. A long side of the transmission filter chip and a long side of the reception filter chip are adjacent to each other.
As disclosed in Japanese Unexamined Patent Application Publication No. 2006-101550, Japanese Unexamined Patent Application Publication No. 2012-205215, and the like, surface acoustic wave chips have been mounted on a package board while considering the propagation directions of the respective surface acoustic waves of the chips. The temperature of an elastic wave device changes influenced by heat emitted from a power amplifier (PA) in use that is disposed in the vicinity of the device, or the like. An elastic wave device using an interdigital transducer (IDT) electrode that is provided in an anisotropic piezoelectric substrate such as LiTaO3, LiNbO3, or the like, has a problem that a change in frequency occurs in the piezoelectric substrate in proportion to a magnitude of thermal deformation.